What if the rounds of silver, copper etc are used only for barter? Barter is not an attempt to establish tender, legal or otherwise. It is simply trade at its most elemental. Like swapping a nail-gun for an old car. Or two families trading baby-sitting services. Or trading a vote for a fridge full of money.
But is the act of barter illegal in your United States? I can see how the IRS would want it to be. But if it isn’t then these people have been robbed.
That is a ‘what if’, but the what if is different than what this group was claiming. They were advertising and selling it as an alternate currency. Currency is the key word. We can what if and compare it to gift cards all day long, but the fraud comes in how it is being sold.